Spaceflight Now: Atlas launch report

AC-141 launch timeline
Posted: Dec. 15, 1999

T-00:02.4 Engine Start
Engine start Atlas booster and sustainer engines are ignited and undergo checkout prior to liftoff. The two ground-start boosters will light a half-second before launch.
T+00:00 Launch
Liftoff Rocket lifts off and begins a vertical rise away from SLC-3E at Vandenberg Air Force Base.
T+00:08 Roll Program
Roll Atlas begins a seven-second roll maneuver to align itself with proper flight azimuth. Following the roll, the vehicle begins open-loop pitch and yaw steering under control of the Centaur inertial guidance system.
T+00:59 Air-lit SRB Ignition
Air-lit The remaining two solid rocket boosters strapped to the Atlas are ignited once onboard computer software determines the two ground-start SRBs have burned out.
T+01:44 Jettison Ground-Lit SRBs
Ground-lit sep The two spent solid rocket boosters that were ignited on the ground are jettisoned to fall into the Pacific Ocean. SRB separation does not occur until the Atlas travels far enough downrange so the boosters land in the allowed Range Safety impact area.
T+01:58 Jettison Air-Lit SRBs
Air-let sep Computer software will determine the air-start solid rocket boosters have burned all their propellant and should be jettisoned from the Atlas vehicle. The two SRBs will fall into the Pacific Ocean.
T+02:46 Booster Engine Cutoff
BECO BECO occurs when axial acceleration of 5.0 g is obtained. Sustainer engine provides the continued boost toward orbit for the Atlas rocket.
T+02:49 Jettison Booster Package
Booster sep The bottom engine structure is separated from the Atlas vehicle.
T+03:11 Jettison Payload Fairing
Fairing separation The 14-foot diameter aluminum payload fairing that protected the Terra spacecraft during launch is separated once heating levels drop to predetermined limits.
T+04:42 Sustainer Engine Cutoff
SECO SECO is commanded once minimum residual propellant is sensed inside the Atlas booster stage.
T+04:44 Atlas/Centaur Separation
Atlas separation Two seconds after the Atlas sustainer engine shuts down, the Atlas booster stage separates from the Centaur upper stage.
T+05:01 Centaur Main Engine Start
MES-1 The single Centaur burn of AC-141 will consist of a 369-second duration firing of the two upper stage engines to inject the combined Centaur and Terra spacecraft into required low-Earth orbit.
T+11:10 Centaur Main Engine Cutoff
Coast The rocket's guidance system will command Centaur cutoff once the proper orbit has been reached. During the burn, guidance steering should have achieved an orbital inclination of 98.31 degrees.
T+11:13 Start Alignment for Separation
Orient The Centaur will orient itself to the correct position for deployment of Terra into space.
T+13:40 Spacecraft Separation
Spacecraft separation Terra, the flagship of NASA's Earth Observing System, is released from the Centaur upper stage to complete the launch.

Image and data source: International Launch Services and Lockheed Martin Astronautics.
Flight data file
Vehicle: Atlas 2AS
Payload: Terra
Launch date: Dec. 16, 1999
Launch window: 1833-1858 GMT (1333-1358 EST)
Launch site: SLC-3E, Vandenberg Air Force Base, Calif.

Pre-launch briefing
Atlas vehicle data - Overview of the rocket that will launch Terra into space.

Terra spacecraft - Facts and information about NASA's Terra satellite.

Pre-launch photo gallery - Follow the rocket and satellite preparations for launch in pictures.

Terra's mission - A NASA release detailing the objectives and science goals of Terra.

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